We have had crackling/dropouts on the snap/2degrees voip phone service for around 6 months or so.
I thought it was our phone, which was dropped, so we threw it out but the replacement was no better.
Today I found an old corded phone to plug directly into the fritz voip port but the dropouts were still occurring. So, it was either the fritzbox or 2degrees.
Gave 2degrees a call, and it is something they know about and they are looking at fixing this from their end although it could take a few days.
In case anyone else has this same issue, give them a call.